The present invention relates to a screw element, in particular for the connection of tubes. The tubes are preferably motor vehicle lines, and are particularly preferably brake lines. A threading and at least one contact surface without threading are provided on the screw element. The screw element has an outer coating and an inner coating. The invention furthermore relates to a tube connection device for the connection of tubes, in particular motor vehicle tubes having such a screw element.
Screw elements, or tube connection devices of the type described above are fundamentally known in the field. In particular screw elements designed as threaded bolts are known, with which tubes from brake lines are connected to assemblies of the brake lines, such as the main brake cylinder, brake pressure distributors or brake power boosters.
These known screw elements are provided with a complete inner coating having a first high friction coefficient. The known screw elements are also provided with an outer coating, which is applied only in the region of the contact surfaces and has a lower friction coefficient than the inner coating. Due to the sliding friction being reduced in this manner during the tightening of the screw element, these screw elements can be tightened to a greater extent, making it more difficult to loosen the screw connection.
These known coatings are applied by means of electroplating, metallization or other methods, which are associated with large time expenditures and high costs.